Toughening mechanism in a ternary polymer alloy: PBT/PC/rubber system

Abstract

The toughening mechanism in a ternary alloy of poly(butylene terephthalate) (PBT), polycarbonate (PC) and rubber is discussed. Transmission electron microscopy (TEM) shows that the ternary alloy has a three-phase structure; fine rubber particles covered with PC shells are dispersed in a PBT matrix. Constructing the corresponding three-phase model for analysis by the finite element method (FEM), we carried out a two-dimensional elastic-plastic analysis of the deformation mechanism. When the model was uniaxially stretched, the rubber particles induced yielding of the PC shell and the PBT matrix and the yielding zone expanded over the whole space at larger strains. This massive yielding of the plastic phases is expected to result in a large amount of energy dissipation and hence the material would be toughened. Using similar analysis of a PBT/PC/void system, the void was shown to play the same role in the toughening mechanism. As expected from the FEM analysis, the three-phase alloy exhibited ductile behaviour in the falling-dart impact test. Both tensile dilatometry and light scattering experiments suggested void formation or cavitation. TEM observation after the impact test clearly supported internal cavitation of the rubber particles. The results suggest that the ternary alloy is transformed to the PBT/PC/void system during deformation, and even after the transformation, the toughening mechanism may persist.